With water temps at 77 your fighting a losing battle IMO. I chill my water using a passive chiller and until I did that I was growing weed but it was subpar and not reaching its full potential. I've tried every additive including shock and my best success was and is hydroguard but I'm sure there are cheaper alternatives. I did use hydrogen peroxide but it's getting hard to find here at 35%, bleach is hard to regulate to the point it is useful and I got rot using EWC tea. Best advice would be chiller and top feed sparingly until roots are established. Also I wonder if your adding enough air if things dried out, popping bubbles should keep things moist.